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I noticed that the soft IRQ thread looked pretty busy under heavy I/O workloads. perf suggested one area that was expensive was the queue_work() call in rpcrdma_wc_receive. That gave me some ideas. Instead of scheduling a separate worker to process RPC Replies, promote the Receive completion handler to IB_POLL_WORKQUEUE, and invoke rpcrdma_reply_handler directly. Note that the poll workqueue is single-threaded. In order to keep memory invalidation from serializing all RPC Replies, handle any necessary invalidation tasks in a separate multi-threaded workqueue. This provides a two-tier scheme, similar to OS I/O interrupt handlers: A fast interrupt handler that schedules the slow handler and re-enables the interrupt, and a slower handler that is invoked for any needed heavy lifting. Benefits include: - One less context switch for RPCs that don't register memory - Receive completion handling is moved out of soft IRQ context to make room for other users of soft IRQ - The same CPU core now DMA syncs and XDR decodes the Receive buffer Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.